Describing the state of public health is an important component of epidemiology, which was presented in Lesson 3.  The next step of comparing outcomes between groups was introduced in Lesson 4.  We saw some examples of situations when the goal is to compare groups, and learned the two main ways to do so:  absolute (differences) and relative (ratios).  An additional point to consider is that the groups may differ on a characteristic that affects the measure, most often age, so standardization is needed in order to make fair comparisons.